Given a discrete subgroup Г of SL(2, ℝ), we consider its action on pseudodifferential operators whose coefficients are holomorphic functions on the Poincaré upper half plane H and construct a vector bundle over the quotient space Г\H whose sections can be identified with pseudodifferential operators invariant under such Г-action.
Paula B. CohenYuri I. ManinDon Zagier
Dan BurgheleaLeonid FriedlanderThomas Kappeler